The present invention relates to a catalytic lacquer for producing printed circuits using basic materials and metal depositing methods.
There is a large number of methods for producing printed circuits. Wide use is made of the so-called subtractive method by which one-side printed circuits and two-side printed boards with through-contact hole connections are produced.
The subtractive method uses one-side or two-side coated carrier material which is subjected to a negative printing method (silkscreen or photo printing). With the through-contact method, the hole walls are occupied by palladium nuclei on which by chemical copper coating, conducting connection of top and bottom side is brought about. The thin copper layer deposited on the hole walls had to be strengthened by a galvanizing process with very ductile copper coatings. Of course, the galvanic copper is deposited not only in the hole walls, but also on the conductor paths. For the subsequent etching process, the printed lines must be covered galvanically with an etch resisting material, e.g., tin- lead or tin.
Prior to the etching of the board, the silkscreen lacquer is removed and the free copper surfaces are etched with etching solution. On the average, depending on the conductive pattern, 60 to 70% of the copper is etched off.
The incidence of such etching solutions containing large amounts of copper is very large and in all cases presents an expensive discharge and pollution problem.
In the majority of procedural steps, the relatively expensive basic material and the underetching of the conductor lines have led to the abandoning of copper coated material and the introduction of a new method.
With the additive method, an adhesive is placed on the plates (German Pat. No. 14 96 984). This adhesive, to ensure adequate adhesion, is chemically pickled, mainly with chrome sulphuric acid (German Laid Open Document No. 16 65 314). Then such a plate is activated in the conventional manner and chemically copper-coated up to 4-5.mu., enclosing possibly required holes. Then, by silkscreen or photo printing, a negative of the desired circuit board is printed and the desired conductive pattern of, e.g. 30.mu. thickness is applied by galvanic copper coating.
The following last steps are the same as with the subtractive method described earlier.
The additive method makes possible the production of much finer conductive patterns since the edging process need only remove the 4-5.mu. chemical copper layer; but this still requires many steps. Also, a plate coated with adhesive must be used which must be first roughened to make the coats to be applied to adhere better.
It is, therefore, an object of the present invention to provide an arrangement making possible the production of printed circuits with fewer steps than the previously known methods.
Another object the present invention is to provide an arrangement of the foregoing character which may be economically fabricated and has stable characteristics while in service.
A further object of the present invention is to provide an arrangement, as described, which has a substantially long service life.